It seems that way. I'm getting no readings at the bias test pins, and nothing happens when I turn both pots in either direction to their stops on both channels. MP101 pin 2 shows 96.9v pin 3 shows -100v. MP102 pin 2 shows 15.5v and pin 3 shows -100. Voltage on pin 2 of MP102 keeps dropping and I notice the right channel LEDs rise to the second from top one when I touch that pin with my probe and the transformer stops buzzing. Looking around I also see some burn marks on R153 and R154. TP5 and 6 still show 100v and -100v.

Rich,Increasingly I've suspected that on this one, my bad back saved it's long time neighbor, my old ass. I wasn't too encouraged when two popped transistors still didn't fix that it. And when I popped two muscles in the old sacrum, now that was discouraging.At least my recovery was linear, uphill. But that poor amp - it can't decide how it wants to f'''k up. Impossible to deal with so many variables over distance. I respect your skill and especially your patience.

Robert R

Hey, I just got a better amp, with that post.Is it possible his amps bias pots are doggie do?

JBJR wrote:It seems that way. I'm getting no readings at the bias test pins, and nothing happens when I turn both pots in either direction to their stops on both channels. MP101 pin 2 shows 96.9v pin 3 shows -100v. MP102 pin 2 shows 15.5v and pin 3 shows -100. Voltage on pin 2 of MP102 keeps dropping and I notice the right channel LEDs rise to the second from top one when I touch that pin with my probe and the transformer stops buzzing. Looking around I also see some burn marks on R153 and R154. TP5 and 6 still show 100v and -100v.

Wow. It looks like both channels are fubar now. Looking back, we started saying 'good channel' and 'bad channel' so long ago I fogot which was which. was the LEFT channel previously good?

regardless, they're both bad now. Perhaps that soldering job you did took some components out, or the loose ribbon cable.

Here's more of the schematic: (harder to read because it's zoomed out):

Capture.JPG (218.77 KiB) Viewed 641 times

Both MP101 and MP102 are giving bad readings. The readings should be symetrical around 0V...you're getting:Left: + 97 and -100RIght: +15 and -100

Burned R153 and R154, to an open? if so, they need replacement, and probably burned through due to excessive current flow (a short somewhere blew something and that is raising the current draw enough to kill the resistors.

Time to do power OFF checks of the resistors and transistors in both bias networks, also around Q107-Q110, and then consider if you'd be better off having it serviced somewhere

Yeah, this thing is driving me crazy. The left channel was the good one. The ribbon cables have been taped, so, they have touched nothing. Checked the soldering and it checks good, never did solder anything on the left channel. I'll go through and check the resistors and transistors in each channel.

Hey Guys, good news, I had a meeting last night and will be returning to work next week !!! It's been a long 2 1/2 months! So Rich as soon as I get some cash together this bad boy will be coming your way!! Hopefully by the end of the month, or the first part of next month!

JBJR wrote:Hey Guys, good news, I had a meeting last night and will be returning to work next week !!! .....

That's good to hear, congrats on getting work; My stepson (a part of the 'Starbucks' generation) was watching TV the other day, and there was a picture from the great depression; the bread lines. He said...."look at those losers". He has no clue what to expect, but hey, he's got his own forum to whine to I guess. If you are younger, I apologize for being so blunt, but I get the feeling that you have a clue, and a work ethic. Good luck to you and yours!

Hey Guys, just an update, I shipped this amp out to Rich which he should have in his hands by the end of the week . Hopefully he can start on it next week and give us a heads up on what he finds while he works his magic on it !!!